At present, in many countries such as German, Japan, England and the United States, a permanent standard time signal is provided by transmitting a radio frequency signal carrying standard time codes by 60-bit time frames. People in those countries can calibrate their apparatus or equipment relevant to time or frequency using the standard time signal. A radio control clock that receives this standard time signal and can read the standard time codes is also provided. The difference between the radio control clock and a conventional clock is that the former can always provide a standard time by automatic time calibration using the standard time signal.
For example, a time frame 10 of a standard time signal provided in Mainflingen, Germany is shown in FIG. 1. The bits of the time frame 10 are transmitted at a rate of 1 bit per minute. In other words, the time frame 10 is transmitted in one minute, which is why we call it Time Frame 1 Minute. The standard time signal carries many time frames in sequence. The standard time code is located from the 15.sup.th to the 59.sup.th bit, which includes the information of the minute, the hour, the day of the week, the month and the year of the standard time. It should be noted that the 0.sup.th to 14.sup.th bit are unused.
Additionally, FIG. 2 is a typical block diagram of a conventional radio control clock 20. The radio control clock 20 includes a signal receive circuit 21, a microprocessor 23, an input device 25 and a display 27. The signal receive circuit 21 may be a satellite, radio frequency or telephone signal depending on the type of the standard time signal. For example, a Time Code Receiver T4225B receives signals at frequencies from 40 to 80 kHz. The microprocessor 23 has a timer (not shown) to keep a current time which is displayed by the display 27. The operation of the radio control clock is described below. First, the signal receive circuit 21 receives a radio frequency signal carrying the standard time and decodes it. Then, the signal receive circuit 21 transfers to the microprocessor 23 a binary code BC representing the standard time derived from the radio frequency signal. The microprocessor 23 performs computations with the binary code BC to correct the current time. The microprocessor 23 can also send a control signal CS to the signal receive circuit 21 so that the signal receive circuit 21 is turned on in response to the control signal CS when time correction is requested. Otherwise, the signal receive circuit 21 is turned off. The input device 25 performs the input of data as needed. For example, before performing the time correction, the microprocessor 23 turns on the signal receive circuit 21 in response to the instructions of the user through the input device 25.
Although the radio control clock can provide the standard time by receiving a standard time signal, it is insufficient in some specific applications. For example, Moslems have five different times of worships a day. Since these times vary with days and seasons, it is difficult for them to have precisely the same five worship times around the world, even though they can have the same current time by using the radio control clock described above. Consequently, in this case, some improvements of the conventional radio control clock are needed.